How can I use a router as a receiver for wireless cameras

It depends on the wireless specification. Router's use the 802.11 wireless standard so the cameras would need to be compatible with that.

You would also need control software for the cameras that allowed you to input the router's wireless key. Without that, you would have to disable wireless security on the router but that would be unwise as anyone within range could use your internet, mess with your router settings etc. without you even knowing about it till it's too late.